Brain stimulation reinforcement (intracranial self-stimulation) has been shown to be comparable to natural reinforcement, and both types are thought to be intimately related to "drive" and "reward" mechanisms. Anatomically, these two mechanisms have been hypothesized to be related to the dopamine (DA)-containing and norepinephrine (NE)-containing neuron systems, respectively. The goal of the present research project is to determine behavioral correlates of central DA and NE unit activity in the rat. Single unit activity is recorded from the DA cells in the ventral mesencephalon, and the NE cells of the locus coeruleus, and correlated with operant responding for a natural reward (i.e., chocolate milk). Such a research project should provide a clearer understanding of the functional significance of the neurons whose malfunctions have been implicated in such disorders as schizophrenia and mania/depression.